A heel-lift is disposed at the end of the heel and makes contact with the walking surface. A heel-lift can be used on a wide variety of shoes, including men's shoes. A dowel-lift is a heel-lift used on women's shoes having at lest a slightly elevated heel. The dowel-lift is molded around a pin or dowel which typically is metal. The dowel projects outward and upward from the dowel-lift. The dowel is driven into the bottom of the heel of the shoe.
For the comfort and safety of the wearer, it is important that the heel-lift have good cushioning and non-slip characteristics. The heel-lift should also have good wear characteristics to extend the life of the shoe.
Prior art dowel-lifts are constructed of a metal dowel and a material having a single hardness, typically a hard thermoplastic polyurethane resin. The hard thermoplastic polyurethane dowel-lift caps off the main part of the heel of the shoe and prevents that main part from being destroyed during normal use.
Hard thermoplastic polyurethane dowel-lifts have several drawbacks. First, the hard thermoplastic polyurethane dowel-lift creates a loud noise when striking a hard walking surface, thereby causing embarrassment to wearers. Moreover, the hard thermoplastic polyurethane has inferior non-slip characteristics. Such inferior non-slip characteristics can result in accidents with injury to the user. Shoe manufacturers have been, and continue to be, involved in numerous lawsuits for damages due to such injuries. Finally, the hard thermoplastic polyurethane has poor wear resistance. Generally, persons in the industry accept that dowel-lifts frequently will need replacement due to wear. In fact, it is a common practice in the industry to include a replacement set of dowel-lifts in the original shoe box so that the woman can replace the dowel lift when worn out.
Another problem with the conventional hard thermoplastic polyurethane has Seen the undesired disengagement of the polyurethane from the metal dowel. Such disengagement can occur when the user pivots on the heel.
Persons in this art have accepted the inferior product because of supposed molding constraints. Persons looked only to conventional hard materials which could be injection molded around a metal dowel. For that reason they accepted the inferior performance characteristics of the hard thermoplastic polyurethane dowel-lifts. The use of the hard material insured that the material adhered to the dowel. It was generally believed that other materials would be inappropriate. Other materials were though to be difficult to adhere to the metal dowel.
Further, the prior art taught that if a soft material was used to contact the walking surface, it was desirable, indeed even necessary, that such softer material be provided in a replaceable form. This was based upon the general belief in the prior art that such softer materials had inferior wear characteristics. Thus, the prior art focussed on the ability to rapidly replace the walking surface contacting piece of a heel lift. See, e.g., French Patent 1,176,647 dated 14 April 1959 to Plouviez.